1. Field of the Invention
The present invention relates to a light guiding film suitable for growing a plant by photosynthesis, and a plant growing method using the light guiding film.
2. Description of the Related Art
Nowadays, there is heightening consciousness of the environment, since if the amount of carbon dioxide, emitted by the use of fossil fuels such as petroleum, increases in the air, the global environment will degrade causing global warming, etc., there will frequently be drought, heavy rain, flooding and the like as well as destruction of the natural environment, natural disasters will arise, agricultural products will be greatly damaged and there will be grave adverse effects on the human society.
Accordingly, as methods for reducing carbon dioxide emitted to the air, methods of applying sunlight to plants such as algae and utilizing the photosynthesis of the plants to reduce carbon dioxide in the air are being examined, and apparatuses to promote photosynthesis of plants are being examined as well.
Regarding the methods for reducing carbon dioxide and the apparatuses to promote photosynthesis of plants, application of light from a light source into a light guiding film through a light entrance portion of the light guiding film is being examined. This light applied into the light guiding film is repeatedly reflected between a light exit surface (upper surface) and a reflective surface (lower surface) of the light guiding film, and when the angle formed between the reflected light and the normal line to the light exit surface is smaller than the critical angle, the reflected light permeates and exits through the light exit surface.
Regarding such a light guiding film, in general, since an opposed light entrance portion positioned on the opposite side to a light entrance portion has flatness, parallel light emitted in the direction perpendicular to a light entrance surface or light whose angle of incidence to an opposed light entrance surface is smaller than the critical angle, among lights emitted from a light source, directly exits to the outside from the opposed light entrance surface side, and thus there is loss of light caused.
Thus, the methods for reducing carbon dioxide and the apparatuses to promote photosynthesis of plants present a problem in which light necessary for the photosynthesis does not sufficiently reach the plants, although the plants may be photosynthesized to some extent.
To solve such a problem, there has, for example, been proposed a method in which light is made to enter from an end of an apparatus, such that the light is guided at a surface portion in an enclosed manner and exits to an intended area (refer to Japanese Utility Model Registration No. 2601449).
However, light which does not enter perpendicularly to the end of the apparatus leaks before a light exit portion instead of being guided to the light exit portion and thus there is a decrease in light extraction efficiency, which is problematic.
Also, there has been proposed a method in which light is guided at a surface portion in an enclosed manner and made to exit to an intended area (refer to Japanese Patent Application Laid-Open (JP-A) No. 2003-215348).
Meanwhile, there has, for example, been proposed a method in relation to a member (e.g., a photosynthesizing member) that converts light into effective matter, wherein the light is made to have such a wavelength as enables highly efficient conversion of the light into the effective matter (refer to JP-A No. 06-38635).
However, there exists the following problem: interfacial reflection arises at a refractive index interface that leads to the converted matter, and thus the light extraction efficiency with which the light is guided to an intended place is low.